The gastrointestinal tract of mammals and humans is populated by a complex microbiological ecosystem, commonly referred to as the intestinal flora, made up of about 400 to 500 different microbial species. The most common of these microorganisms are those belonging to the genus Bacteroides, including Bifidobacterium, Eubacterium and Fusobacterium.
The structure and function of the gastrointestinal tract and its metabolic activity are closely dependent on the presence of appropriate intestinal flora, which play a very important role in normal physiological processes and are also involved in some pathological conditions. Among other things, the intestinal flora provide protection for the body against gastrointestinal infections caused by pathogenic microorganisms.
When the composition of the intestinal flora is changed, as is the case, for instance, following therapeutic administration of antibiotics, various intestinal disorders may result, such as, for example, nausea, vomiting, colitis and diarrhoea.
To ameliorate these conditions, orally administrable pharmaceutical preparations containing Bacillus subtilis spores are normally prescribed, usually as a liquid suspension. It is intended that, upon oral administration, the spores will survive the acid environment of the stomach (pH 1 to 2) and reach the intestine (pH 6 to 8), where they will convert into vegetative forms capable of replication. However, the phenomenon of spore activation that produces the vegetative cells, being affected by the exposure to particular nutritional an chemical-physical conditions, is highly variable and depends on individual factors. Therefore it is difficult to control this phenomenon. Normally, at least one billion spores of Bacillus subtilis per dose are administered to ensure subsequent proliferation of a small fraction of the administered organisms in the human intestine. This approach, however, is economically wasteful and therapeutically suspect, since an unpredictable amount of live bacilli are delivered to their site of action in the intestine. Thus, there is a need in the art for methods and compositions that shield microorganisms from the gastric environment, while preserving their viability, and allow the administration of more precisely defined doses.
Other microorganisms that are administered for therapeutic purposes include lactic bacteria, e.g., Bifidobacterium longum, Lactobacillus acidophilus, Lactobacillus bulgaricus, Streptococcus lactis, Streptococcus thermophilus, and the like (Topley and Wilson,: Principles of Bacteriology and Immunity, E. Arnold, Ed., London, 1966). U.S. Pat. No. 4,946,791 describes novel strains of Lactobacillus acidophilus that are particularly useful due to their ability to adhere to the intestinal epithelia of different animal species.
In addition to components of the intestinal flora, enzymes that may serve important medical and/or nutritional functions may also be adversely affected by the gastric environment and/or the environment of other media wherein such enzymes may be incorporated. Examples of enzymes commonly used by the food industry are lipases, esterases, pectinases (which are used in the fruit-juice and wine industries), amylase, glucoamylase, and lactase.
Lactase, which is used in the dairy industry to hydrolyse lactose into its components glucose and galactose, also has a particular medical significance. Some individuals are "allergic" to cow's milk, and this phenomenon is related to genetic background as well as dietary habits. Milk "allergies," which appear in 40% of Asian countries and 15% of European populations, most commonly reflect lactose intolerance. This syndrome is caused by a deficiency of the enzyme .beta.-galactosidase (lactase), which is normally secreted by epithelial cells in the small intestine. In lactase deficiency, lactose remains undigested and is not absorbed. In the small intestine, the high concentration of unabsorbed lactose draws water osmotically into the jejunum, and acts in the colon as a substrate for gas-producing coliform flora. This set of actions causes swelling and diarrhoea, which may occur from a few hours up to 12 hours after ingestion of milk. Lactose intolerance first appears at approximately ten years of age in Caucasians, and much earlier, at approximately 2-3 years, in other races in which the phenomenon is more prevalent.
Additionally, when milk is prophylactically removed from the diet of such affected individuals, even their low level of .beta.-galactosidase production is further reduced, thus exacerbating the phenomenon of intolerance.
The phenomenon of widespread lactose intolerance has promoted the development of processes to modify or remove lactose from milk. Some of the most successful processes are based on the use of immobilized enzymes capable of fully hydrolysing milk lactose, making the milk digestible and assimilable even by lactose-intolerant individuals.
However, a drawback to the administration of biologically active compounds such as enzymes is their lability and sensitivity to environmental conditions such as pH. For instance, pancreatic lipase is completely denatured (and thus inactivated) at pH values lower than 4; conversely, the enzyme is maximally active only at pH values higher than 6.
In general, it would be predicted that enzymes sensitive to an acid environment would be ineffective when added to foods having acid pHs, such as, for instance, yoghurt and fruit juices. Furthermore, a natural barrier for products meant for nutritional administration is the gastric tract, where both the extreme acidic pH, as well as endogenous digestive enzymes, may inactivate biological food additives.
One approach to minimizing losses of active material is to encase the active compound in an enteric coating. For example, EP 583,726 teaches enterically coatable pancreatin micropellets, and JP 04 411,434 (CA 116:241966) teaches tablets containing Lactobacillus acidophilus coated with intestinally soluble substances. The main drawback of these teachings is related to the particle size of the preparations (pellets, tablets) which makes them unsuitable for a suspension in liquid or semiliquid foods.
U.S. Pat. No. 5,296,236 ('236 patent) describes a therapeutic system for suspension in liquid consisting of microgranules containing a pharmaceutical ingredient and coated with multiple layers of filming material that allow controlled-release of the active ingredient. The methods and compositions described in the '236 patent, however, are designed for self-contained controlled-release pharmaceutical liquid formulations and not for food additives which need not necessarily be delivered to their use point in a sustained release fashion but which must be protected from an adverse environment for extended periods of time. Furthermore, the methods and compositions are not applicable to microorganisms, which are too large to diffuse from microgranules in a manner that insures controlled-release.
It is thus an object of the present invention to provide methods and compositions that allow the addition of beneficial acid-labile or protease-sensitive biological compounds and microorganisms to ingestible materials such as foodstuffs, especially fluid and semi-fluid foods, while (a) maintaining (as long as is dictated by the particular foodstuff) the bioactivity of the compounds or organisms in an environment (either in the formulation or at the use point, or both) which is adverse to said bioactivity; and (b) creating stable suspensions of the additive(s) in ingestible materials, particularly foodstuffs, that permit administration of defined amounts of additives to consumers of foodstuffs.
The present inventor has now found that granulating and coating technology developed for the production of pharmaceutical dosage forms (as described, e.g., in the '236 patent) is particularly useful for preparing foodstuffs supplemented with microorganisms or other bioactive compounds. In particular, coated microgranules containing a biologically active material that are prepared according to the present invention are of sufficiently small size that they can be homogeneously suspended in fluid or semi-fluid foods.